Method for forming rupture disc

ABSTRACT

A rupture disc system comprises a rupture disc including a dome portion and a flange portion interconnected by a transition region and a mounting mechanism for mounting the rupture disc by the flange portion thereof in a pressure relieving vent. The rupture disc includes a thickness reducing groove at least partially circumferentially surrounding the dome portion and located in the transition region thereof. Preferably, the rupture disc is of the reverse buckling type and the groove does not completely surround the dome portion so as to define a tab or hinge within that part of the transition region which is ungrooved or not as deeply grooved as a remainder of the transition region. In addition, the slope or radius of curvature may be increased in the region of the tab. The rupture disc also includes an indentation on the dome portion. The indentation is preferably greatest on the dome portion at a location spaced from the transition region and directly between the tab and a crown of the dome portion. In addition, the mounting mechanism includes a lower ring member having an arcuate projection which extends into the vent. Preferably, the arcuate projection is located so as to be relatively close to and so as to align with the tab such that the dome portion wraps about the projection when reverse buckling and rupture occurs. Methods are disclosed for producing the disc with the groove and the indentation.

BACKGROUND OF THE INVENTION

The present invention relates to safety pressure relief devices and, inparticular, to rupture discs, especially reverse buckling rupture discs,and also to methods of manufacturing such discs and of producingfailures in such discs which are highly predictable.

Relief devices of the type commonly known as rupture discs have beenutilized by industry for many years to provide a safety mechanism torelieve excessive pressure from an overpressurized system or vessel in areliable manner. The rupture disc is most frequently placed in a ventfor a pressure vessel or the like so as to prevent flow of fluid throughthe vent until the disc ruptures. Through the years, numerousimprovements have been made in the rupture disc concept in order toreduce the cost and to improve the reliability of the disc.

A specific type of disc normally referred to as a reverse bucklingrupture disc has also been utilized for a number of years and functionsunder the principle that a dome is formed in the disc which ispositioned in the vent such that the dome points toward or faces thepressure side of the vent, that is, the convex side of the dome facesthe internal portion or upstream side of the vent wherein pressurizedfluid is likely to produce an overpressure which would be dangerous ordestructive if not relieved. One advantage of reverse buckling typediscs is that systems being protected by the discs can be operated atpressures relatively close to the bursting pressure of the disc withoutproducing fatigue and failure which occurs in many forward burstingdiscs when operated for long periods of time near the rated burstingpressure of such discs. The dome, when fluid pressure reaches apreselected pressure for which the dome was designed to rupture, startsto collapse, that is, the column or arch of the dome on one side thereofstarts to buckle. It is believed that as the arch on one side of thedome starts to collapse, a buckling type wave typically propagatesacross the surface of the dome to the opposite side of the dome wheretotal collapse eventually occurs. This buckling wave tends to create awhiplash effect on this opposite side of the dome so that the dome atthis location is rather violently urged in the direction to which theconcave portion of the dome faces (that is, the downstream side of thevent). Many of the reverse buckling rupture discs include knife bladespositioned on the concave side of the dome which are normally in spacedrelationship to the dome but which are engaged by the dome uponbuckling. The knives cut the dome, typically in such a pattern as tocause petals which are held to a flange portion of the disc by tabregions or the like.

Knife blade assemblies for reverse buckling rupture discs addsubstantially to the cost of such discs and are subject to failure dueto corrosive activities of the fluids within the vent system, damageduring handling or simply because a mechanic forgets to install theknife assembly which in normal discs results in disc bursting pressuresthat are many times the rated pressures of such discs. It has,therefore, been a goal of the rupture disc industry to produce a disc ofthe reverse buckling type which does not include knife assemblies, butwhich is highly reliable. One reverse buckling rupture disc, which wasspecifically designed to rupture without the use of knife blades,incorporates the concept of placing grooves, scores or etchings,especially in criss-cross or circular patterns on concave or convexfaces of a reverse buckling rupture disc dome. A dome of this type canbe seen in U.S. Pat. No. 3,484,817 of Wood. In the Wood device therupture disc dome buckles, reverses and fractures along the lines ofweakness produced by the grooves so as to form petals which are held tothe remainder of the rupture disc assembly.

There has been a continuing desire in the rupture disc industry toproduce new types of reverse buckling rupture discs which haveproperties that make them especially suitable for specific purposes,more cost efficient, and/or make the disc more reliable. In particular,new reverse buckling rupture discs are desired which will functionwithout the need for knife blades for cutting the disc on reversal, yetwhich will remain highly reliable so as to relieve within a relativelyclose tolerance of the predetermined rupture pressure necessary toprotect the vessels or the like which are protected by the disc.

There has also been a problem associated with some reverse bucklingrupture discs which do not have knife blade assemblies in that the disccan accidentally be inserted into the vent system with the concave sidefacing in the wrong direction. Therefore, it is important that therupture disc relieve in either direction, although the relief in thebackwards direction may normally be at a higher pressure.

There is also a problem in some systems with portions of the rupturedisc being entrained with the fluid being relieved. Pieces of rupturediscs can cause damage to pumps and the like if they are allowed tofreely break away from the remainder of the rupture disc assembly uponrupture. Therefore, it is important that the rupture disc dome or petalsof the rupture disc dome remain intact after rupture and that theyremain attached to a remainder of the disc.

OBJECTS OF THE INVENTION

Therefore, the principal objects of the present invention are: toprovide a rupture disc system which is highly reliable such that therupture disc associated with the system ruptures within a relativelyclose range on either side of a preselected pressure to protect a vesselor the like from overpressure; to provide such a system including areverse buckling rupture disc which does not require a knife assembly toopen; to provide such a reverse buckling rupture disc which willreliably rupture at a first given pressure when fluid pressure isapplied to the convex side thereof and at a second given pressure, forexample 1.5 times the first given pressure, when fluid pressure isapplied to the concave side thereof; to provide such a rupture discincluding hinge or tab means for retaining the disc or portions of thedisc with the remainder of the rupture disc assembly after rupture ofthe disc; to provide a structural configuration of the disc whichensures that the disc will first fail on the side of the disc associatedwith the hinge or tab and therefore first tear between a dome and flangeportion of the disc opposite such hinge or tab and thereafter tear tothe edge of said tab leaving the hinge or tab intact; to provide such adisc having indentations or dimples spaced from the hinge or tab regionin the dome, especially on the dome directly and between the tab regionand a crown of the dome, so as to initially trigger failure or bucklingof the rupture disc adjacent to the tab or hinge; to provide such areverse buckling rupture disc having a change in radius in a transitionregion between the disc dome and flange portions adjacent the tab orhinge region so as to ensure initial failure or buckling of the disc inthe region of the dome directly between the tab region and the domecrown; to provide such a disc utilizing an arcuate projection into thevent assembly opposite the concave side of such disc and spaced closelyadjacent the hinge or tab region of the disc for the dome to wrap aboutafter rupture thereof; to provide such a disc having a groove or etchingin the transition region between the dome and the flange portion of thedisc; to provide such a groove or etching which is approximatelytwo-thirds the depth of the transition region; to provide such a dischaving a groove which extends only partially about the transition regionand defines the tab or hinge region thereof within the portion of thetransition region wherein the grooving or etching does not occur; toprovide such a system including support rings on either side of theflange portion of the rupture disc which cooperate with the disc toensure that the grooved area in the transition region is supported onthe concave or downstream side of the rupture disc dome and that therupture disc is also free to fracture toward the convex side thereofwithout being held in place or restricted from buckling by the supportring on that side after rupture; to provide a method of manufacturingsuch a rupture disc having a groove in the transition region including amethod and apparatus for producing the groove; to provide a method forforming an indentation on the side of the rupture disc dome associatedwith a hinge or tab; to provide a method of producing a rupture disc ofthe type described having a transition region with a portion thereofassociated with a tab region having a greater radius than the remainderthereof, so as to provide a first buckling area, in the tab region; toprovide a method of placing a continuous circular groove in thetransition region between a dome and a flange portion of the rupturedisc with varying depths so as to define a tab region; and to provide anoverall rupture disc system which is relatively economical tomanufacture, convenient to install, highly reliable, and particularywell adapted for the intended usage thereof.

Other objects and advantages of this invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

SUMMARY OF THE INVENTION

A rupture disc assembly is provided which includes a domed or pre-bulgedrupture disc of the type utilized to protect pressure vessels or thelike from over pressure. The rupture disc is preferably a reversebuckling disc, but certain of the improvements discussed hereinafter maybe utilized in conjunction with a conventional forwardly opening disc.The improvements discussed herein derive from experimentation directedto finding a rupture disc which would not only relieve at a preselectedpressure (normally the preselected pressure is approximately 2/3 of themaximum rated rupture pressure associated with the vessel or otherprocessing equipment to be protected by the disc), but also wouldrelieve at a second preselected pressure, if the rupture disc wereinadvertently installed backwards (such second pressure for examplebeing approximately the maximum rated pressure of the vessel, again forexample, at a pressure 1.5 times the first preselected pressure).

It was especially desired to produce a reliable reverse buckling rupturedisc which would predictably rupture at such a first preselectedpressure, and which would also rupture at said second preselectedpressure if the disc were inadvertently placed in the vent linebackwards, and further that the disc should rupture without the aid of aknife assembly as knife assemblies are expensive and may be susceptibleto corrosion, damage, and the like which produces failure in the suchknives or the knife blades may be accidentally left out of the assemblyduring installation.

With this in mind, numerous structures were tested but failed to havethe predictable rupture pressures required of such devices. Contrary toconventional thought in the rupture disc industry against making anymodifications in the region of the reverse buckling rupture disc betweendome and flange portions (normally referred to as a transition area orregion), other than to change the radius thereof, it was discovered thatplacing of a groove within the transition area produced suitable andhighly repeatable release pressures in either direction.

A full circle groove in the transition area of a reverse bucklingrupture disc produced highly repeatable results when the groove wasmanufactured in a consistent fashion. It is noted that the groove mayaffect the bursting pressure of the disc as compared to the disc beforethe groove is added, however, the important result with the groove aswith other improvements discussed herein, is that the bursting pressurebe consistently reproduceable in successive discs which are modified orproduced in the same manner.

It was found that a satisfactory groove could be made by placing a diewith a knife edge under pressure against the transition area andallowing the knife edge to penetrate the area. It was found that aparticular knife blade had to be tested with each different disc to seeif that blade was compatible with the disc. For example, flatter or ovaledged knife blades were found to be suitable for discs which arethicker, while more V-shaped knife blades with a radius from about 0.003to 0.015 on the edge were found to be better for relatively thinnerdiscs. One suitable V-shaped knife blade for certain rupture discs wasfound to be a blade having in cross section a central axis which isperpendicularly aligned with the surface of the flange portion of thedisc when forming the groove, sides of the block which diverge generallyfrom the central axis and specifically from a point or knife edge atangles of approximately thirty degrees, and an edge which had a radiusof approximately 0.005 inches. The radially inner side of the knifeblade is preferably placed close to or adjacent the domed portion of thedisc and it is not unusual for the radius of curvature of the dome atits juncture with the transition region to change during manufacture ofthe groove. While the exact depth of penetration of the knife blade intothe transition area varies with the desired bursting pressure in eachdirection, thickness of the disc and with materials of construction, itwas found in some discs that a groove depth of approximately two-thirdsthe thickness of the transition area is often quite suitable forproducing the effect of bursting at the first preselected pressure inone direction and bursting at a pressure approximately 1.5 times thefirst preselected pressure in the opposite direction, if the disc wereinadvertently installed backwards. A groove depth of 40 to 50% of thedisc normal thickness was often found to be sufficient to producetearing upon buckling in most discs. However, it is specifically notedthat depths of the groove cited herein are for purposes of example andthat the depth required for a certain disc (that is a specific dischaving a fixed thickness, material of construction, temper, etc.) torelieve at a certain pressure can only best be determined byexperimentation. It is important that the reverse buckling rupture discwith the groove in the transition area be supported on the downstreamside thereof (that is, on the side of the disc where fluid pressurewould normally not be applied and also on what would normally be theconcave side of the dome portion of the disc). The structure supportingthe rupture disc in this manner preferably extends along substantiallythe entire portion of the transition area, especially where grooved.When reference is made herein to the groove being "in the transitionarea", it is meant that it is placed on the disc in such a manner as itwould at least touch the original transition area. Actually, a modifiedtransition region is normally formed when the groove is placed on thedisc.

While the full circle grooving in the transition region works well forreverse buckling rupture discs wherein it does not matter if fragmentsof the ruptured disc are carried downstream in the vent line after therupture disc bursts, it is often desirable to retain the rupture disc asan integral, although ruptured, unit even after bursting. For this, ahinge or tab is placed between the dome portion and the flange portionof the rupture disc. One method to provide such a tab, is that groovingis applied to the transition region in a partial circumferential mannerso as to define such a tab region by that portion of the transitionregion which has not been grooved. For example, a thirty degree arc ofthe transition region may be left ungrooved while a continuous 330degree remaining arc is grooved. Tabs of larger and smaller area havebeen found to be functional and the optimum tab arc depends on theparticular disc.

While producing a tab region by not grooving a certain portion of thedisc on the transition region functions well for certain discs andutilizations, it is found that normally the larger the ungrooved area,then the more unpredictable the bursting pressure of the disc becomes.In addition, in certain discs the violence of the rupture will cause atear through such a tab region. It was found that a disc with a morereliable bursting pressure and yet with a tab region could bemanufactured by utilizing a die with a generally continuous or full 360degree arc knife, by changing the characteristics of the knife in theregion desired to be left as a tab.

In particular, a portion of the knife edge is removed corresponding tothe desired size of the tab, such that during the grooving process theknife does not form a groove in that portion where the edge is modifiedor at least does not form as deep a groove in the projected tab portion.The knife blade does apparently change the radius of curvature of thetransition region adjacent the projected tab area even though it is notas deeply grooved, if at all; and, while applicant does not wish to berestricted to a certain theory of operation, it is believed that thischange in radius modifies the characteristics of the disc in such amanner as to produce a disc which relieves at a more predictablepressure. Preferably, the knife blade is placed on the disc flangeportion upstream flat surface next to the dome portion, and thereafterpressure is applied to the blade to urge it to penetrate into the flangeportion along the transition region and, in particular, in a manner soas to penetrate generally perpendicular to the flat sides of the flangeportion. It is noted that the maximum depth of penetration of the knifeblade in the transition region is preferably accurately controlled byuse of the stops or the like.

It is generally believed in the industry that reverse buckling rupturediscs tend to collapse or buckle on one side of the dome at which time abuckling type wave propagates out over the top of the dome to theopposite side of the dome. As the wave hits the opposite side of thedome there is a whiplash effect which violently thrusts the side of thedome associated with such whiplash in a downstream direction and tearsthe dome from the flange portion, which tear then propogates back aroundthe disc to the side where the buckling first occurred. This whiplashbuckling effect is often sufficiently strong to break the tab region ofthe rupture disc, if failure of the disc first occurs opposite such tab.Therefore, in order to provide even more reliability to the tab in orderto prevent fragmentation of the disc, it is desired to first initiatefailure of the disc in the tab region so that the whiplash effect willoccur opposite the tab region.

A suitable technique for inducing failure of the disc first in the areaof the dome in close association with the tab region has been found tocomprise substantially modifying the radius of curvature of thetransition area adjacent (that is coextensive with) the tab region oradjacent a portion of the tab region. Pre-bulged rupture discs are oftenmanufactured by applying fluid pressure to one side of flat plate ofsheet metal stock while supporting the opposite side of the stockagainst a forming ring, the interior diameter of the forming ringdefines the chordal diameter of the dome of the disc to be formed in theplane of the projected flange portion. The disc thus domes up throughthe forming ring. The edge of the forming ring is normally a fairlysharp 90 degree angle which forms a specific radius of curvature at thetransition area. By breaking or rounding the radially internal edge ofthe ring where it engages the disc with a whetstone or the like, theradius of curvature of the transition area of the resulting rupture discvaries where such rounding occurs in the forming ring as compared towhere no rounding has occurred. In this way the radius of curvature canbe increased along that portion of the transition area of the discassociated with the tab region to ensure initial failure of the dome inclose proximity to the tab region (especially on an arc of the domewhich is centered on the tab region and extends to near the dome crown).

A second method has also been found for inducing the initial failure ofthe dome at or relatively near a selected location. This second methodcomprises placement of a dent, dimple, or other deformation, which willgenerally be referred to herein as an indentation, in the dome itself ata location spaced from the transition region and further in spacedrelationship to the crown of the rupture disc but in close proximity tothe projected tab region. Preferably, the center of the indentation isdirectly on an arc of the dome extending between the top or crown of thedome and the tab region, that is located on the dome on an arc directlyconnecting the center of the tab with the dome crown. Such anindentation may take the form of a dot, an elongate chord or arc runninggenerally parallel to the transition region of the disc, a series ofdots or lines defining indentations, or the like. It has been found thatthe failure of the dome may occur anywhere along the indentation;therefore, a relatively short indentation, for example not exceedingthirty degrees in arc, may be desirable for certain applications butlarger indentations do function to ensure failure somewhere along theindentation. It is preferred that the indentation not substantiallyreduce the wall thickness of the dome and that it be placedunsymmetrically with respect to the dome. The height of the placement ofthe indentation relative to the overall height of the dome may vary inaccordance with the desired failure pressure (typically, the closer tothe crown, the greater reduction in rupture pressure for a particulardisc). A suitable height for an indentation has been found to be, forexample, approximately 0.06 inches from the transition region for somediscs. Again optimum shape and placement of the indentation for aparticular disc is found by testing.

Suitable indentations can be produced in the dome by placing an edge orpoint against the dome at the desired location while applying pressureto the opposite side of the dome. This can advantageously beaccomplished in conjunction with the pre-bulging of the disc. Inparticular, a second indentation ring may be used adjacent the bulgeforming ring which forming ring defines the perimeter of the dome duringformation thereof. Such an indentation ring rests atop the bulge formingring and has an edge or point against which the dome is urged duringformation thereof. Spacing of the indentation ring from the flangeportion is controlled by the thickness of the forming ring. Suitabletypes of rings have been found to include a circular ring which has thesame interior diameter as but is slightly non-concentrically alignedwith the bulge forming ring so as to place a dent in the dome at thelocation above or in close association with the projected tab region.Other rings include those concentrically aligning with the bulge formingring but having a curved or linear edge on the radially inner side of aprojection extending radially inwardly from the ring. It has been foundthat the relief pressure of the disc varies significantly with whichtype of indentation ring is utilized so again testing must be used tofind the relief pressure of a given disc with a specific indentation,but, if all factors remain the same for consecutive discs, then eachshould relieve at the same pressure. The indentation can also be formedin a procedure separate from the pre-bulging procedure.

Finally, it has been found that the force associated with rupture ofcertain discs will tear the tab region, even when initial failure of thedisc is on the side of the dome associated with the tab region. It hasbeen found that, if an arcuate projection extending radially inward fromthe side of the vent below the tab region is provided for the dome towrap about upon rupture while the tab is still intact, then the tabregion is less likely to tear. When it is indicated herein that theprojection is below or aligned with the tab region, it is meant that theprojection should be downstream in the vent relative to the unruptureddisc, on the concave side of the rupture disc prior to rupture, andcould refer to such a projection which was actually spacially "above"the disc but still downstream from same. In particular, the projectionshould be aligned such that as the dome pivots about the hinge formed bythe tab region upon rupture, the dome engages the projection.Projections which have a linear or chordal engaging surface have beenpreviously used in the art, but have been found to sometimes allow thedome to continue to rip along the tab region and, therefore, were notgenerally found to be satisfactory for the disc described herein. On theother hand, projections which are relatively arcuate in nature andproject radially inward from the side of the vent, especially those thatare almost circular or nearly approximating the curvature of the domewere found to be most suitable.

A suitable projection for certain uses was found to be one that isgenerally flat on sides thereof facing toward and away from the rupturedisc prior to bursting and which has the facing surface in a plane whichis generally adjacent a plane defined by the downstream side of theflange portion. Further, the example projection has a thickness ofapproximately 0.060 inches, has a radially inwardly projecting edgewhich is almost circular, and has a radius roughly between one-fourthand one-fifth the radius of the inner diameter of the disc flangeportion. The example projection being attached to and extending along adownstream support ring for the disc through an arc length which ispreferably slightly longer than the arc length associated with the tabregion. For example, if the arc of the tab region is approximately 30degrees, then the projection would extend for an arc of approximately 34degrees. In this manner, the transition area of the disc tears along thegroove upon rupture to the tab region and such that the edges of thedome next to the tab region do not align exactly with the projection buttend to wrap thereabout so as to further secure the ruptured dome to theprojection until a maintenance crew can change the disc.

While the improvements discussed above have been described especially interms of reverse buckling rupture discs, certain features of theimprovements can be utilized in conjunction with other types ofconventional rupture discs. In particular, it is foreseen that acircumferential groove may be utilized in a transition region of aconventional forward failure rupture pre-bulged disc to allow a failureif the disc is inserted backward and may be utilized in conjunction withtypical grooves, slits or other devices on the dome of such forwardacting disc which grooves, etc. cause failure in a normal forwarddirection.

It is noted that in some of the drawings, the scale of certain featureshave been exaggerated, where necessary, in order to show detailsthereof. This is especially true of the thickness of the various rupturediscs relative to the assembly associated therewith. The drawingsconstitute a part of this specification and include exemplaryembodiments of the present invention and illustrate various objects andfeatures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a rupture disc assembly accordingto the present invention installed in a vent pipe between support ringswith portions broken away to illustrate details of the assembly.

FIG. 2 is a top plan view of the rupture disc and support rings of FIG.1 with portions of the lower support ring shown in phantom.

FIG. 3 is an enlarged, fragmentary cross-sectional view of the rupturedisc and support rings taken along line 3--3 of FIG. 2.

FIG. 4 is an enlarged, fragmentary cross-sectional view of the rupturedisc and support rings taken along line 4--4 of FIG. 2.

FIG. 5 is an exploded cross-sectional view of the assembly shown in FIG.1.

FIG. 6 is a separated perspective view of the rupture disc and the lowersupport ring at a reduced scale.

FIG. 7 is a fragmentary cross-sectional view of the rupture discassembly shown in FIG. 1 after rupture of the rupture disc.

FIG. 8 is a top plan view of a first modified rupture disc and supportring therefor for use in conjunction with the rupture disc assembly ofFIG. 1, with portions broken away to show the support ring in greaterdetail.

FIG. 9 is an enlarged fragmentary cross-sectional view of the firstmodified rupture disc taken along line 9--9 of FIG. 8.

FIG. 10 is a side elevational view of the first modified rupture disc.

FIG. 11 is a perspective view of the first modified rupture disc andsupport ring thereof showing details of the disc and ring in phantom.

FIG. 12 is a perspective view of a second modified rupture disc andsupport ring therefor for use in the rupture disc assembly shown in FIG.1.

FIG. 13 is a an enlarged fragmentary cross-sectional view of the secondmodified rupture disc and support ring taken along line 13--13 of FIG.12.

FIG. 14 is a top plan view showing a third modified rupture disc for usein conjunction with the rupture disc assembly of FIG. 1.

FIG. 15 is an enlarged fragmentary cross-sectional view of a fourthmodified rupture disc for use in the rupture disc assembly of FIG. 1.

FIG. 16 is a perspective view at a reduced scale of a planar blank ofmaterial to be formed into a reverse buckling rupture disc according tothe present invention.

FIG. 17 is a perspective view showing a reverse buckling rupture discproduced from the blank of FIG. 16 just following the formation of abulge at a central portion of the disc and showing a die ring throughwhich the bulge is formed with portions of the ring broken away to showdetail thereof.

FIG. 18 is an exploded cross-sectional view of a rupture disc and agrooving apparatus having a knife blade die for placing acircumferential groove in the transition area between flange and domeportions of the disc.

FIG. 19 is an enlarged fragmentary cross-sectional view of the apparatusand disc of FIG. 18 showing the disc during the actual process step offorming a groove in the transition area thereof.

FIG. 20 is an exploded perspective view at a reduced scale of a rupturedisc and the die from the grooving apparatus shown in FIG. 18 followingetching of the disc in the transition area.

FIG. 21 is an enlarged fragmentary cross-sectional view of a reversebuckling disc during a step in a manufacturing process wherein the domeof the disc is urged upward through a forming ring.

FIG. 22 is a view similar to FIG. 21 at a different location around thering and showing a change in the radius of the transition areaassociated with the rupture disc.

FIG. 23 is an exploded perspective view at a reduced scale of a rupturedisc with upper and lower supporting rings during another step in theprocess of manufacturing of an assembly such as is shown in FIG. 1.

FIG. 24 is an enlarged fragmentary cross-sectional view of the rupturedisc and the support rings of FIG. 23 after spot welding same together.

FIG. 25 is a fragmentary cross-sectional view similar to that of FIG. 24but further enlarged in comparison and showing a rupture disc andsupport ring for use in the assembly of FIG. 1 and illustrates a groovein the transition region between the dome and flange area thereof.

FIG. 26 is a top plan view of the rupture disc and ring assembly shownin FIG. 23 with portions broken away to show detail thereof.

FIG. 27a is a top plan view of a dome forming a ringlet set for use in astep in the process of forming a reverse buckling rupture disc with anindentation on a dome thereof.

FIG. 27b is a view similar to FIG. 27a and illustrates a first modifieddome formation ringlet set for forming a first modified indentation on arupture disc during a process in the manufacture thereof.

FIG. 27c is a view similar to FIG. 27a and shows a second modifiedindentation formation ringlet set for forming a second modifiedindentation on a rupture disc.

FIG. 28a is a top plan view showing a fifth modified rupture disc havingan indentation formed thereon by the ringlet set shown in FIG. 27a.

FIG. 28b is a view similar to FIG. 28a showing a sixth modified rupturedisc having an indentation formed thereon by the ringlet set shown inFIG. 27b.

FIG. 28c is a view similar to FIG. 28a showing a seventh modifiedrupture disc having an indentation formed thereon by the ringlet setshown in FIG. 27c.

FIG. 29 is a cross-sectional view of a rupture disc during a step in theprocess of manufacture thereof and shown in a rupture disc bulge formingapparatus suitable for use alternatively with the ringlet sets shown inFIGS. 27a, 27b and 27c for the formation of an indentation on therupture disc.

FIG. 30 is a cross-sectional view of a rupture disc similar to the discshown in FIG. 29 but having an indentation formed thereon by the ringletset of FIG. 27a.

FIG. 31 is a perspective view of a modified grooving apparatus knifeholding member similar to the die of FIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosedherein, however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure.

The reference numeral 1 generally designates a safety pressure reliefassembly according to the present invention. The assembly 1, as is bestseen in FIG. 1 and in the exploded view in FIG. 5, is secured betweenopposite flanges 2 and 3 which are end flanges of vent pipe sections 4and 5 respectively and which are securely held together so as to clampthe assembly 1 therebetween by a plurality of circumferentially spacedbolts 6. The vent pipe sections 4 and 5 form part of a vent systemincluding an interior channel 8. The vent system includes an upstreamportion which is associated with vent pipe section 4 and which joinswith a pressure vessel or the like (not shown) to be protected by thevent system and would also normally be the side of the vent system to bepositively pressurized by fluid therein. Vent pipe section 5 dischargesto a safe location (not shown) to relieve excess pressure communicatingtherewith from vent pipe section 4 upon relief by the assembly 1. Theassembly 1 comprises a downstream support structure 11 (FIG. 5), adownstream seal member 12, an upstream support structure 13, and anupstream seal member 14. The assembly 1 further comprises a downstreamsupport ring 16, and upstream support ring 17, and a reverse bucklingrupture disc 18.

When the assembly 1 is in use, seal member 14, the support structure 13,the support ring 17, the rupture disc 18, the support ring 16, thesupport structure 11, and seal member 12 are in sequential, abutting andsnug relationship with respect to one another so as to be generallyresistant to fluid pressure leaks in a radially outward direction, thisconfiguration being shown in FIG. 1. The assembly 1 is retained togetherby keeper brackets 20 and 21 which are secured to both of the supportstructures 11 and 13 by suitable bolts (not shown) or the like receivedin threaded apertures 23. There is a generally unrestricted upstreamchannel portion 24 extending from the upstream or convex side 27 of therupture disc 18 to the vessel or the like being protected by theassembly 1 and a generally unrestricted downstream channel portion 25extending from a downstream or concave side 28 of the rupture disc 18.The downstream support structure 11 includes an annular seat 30 for thesupport ring 16 and further includes an annular boss 31 which ispositioned radially inward from the seat 30. The boss 31 extendscircumferentially in conjunction with the seat 30 except for a sector 32of the seat which angularly aligns with an arcuate projection 34 on thesupport ring 16.

Attention is directed to the support rings 16 and 17 and the rupturedisc 18, such as are shown in greater detail in FIGS. 2, 3, 4 and 6. Therupture disc 18 is of the type commonly referred to as a reversebuckling rupture disc having a central pre-bulged dome 40, a generallyplanar flange portion 41 which extends radially outward from a peripheryof the dome 40, and a transition area or region 42 between the dome 40and the flange portion 41. The dome 40 has the disc convex side 27 andconcave side 28 thereon, an apex or crown 43 and has a generally uniformthickness, although the thickness normally varies somewhat due tovariances induced during the pre-bulging of the dome 40.

The rupture disc 18 further includes a semi-circular groove 44 which isin the transition region 42. A portion of the transition region 42generally indicated by the reference numeral 45 does not include agroove therein and is a projected or designated hinge or tab region forthe rupture disc 18 at the time of bursting. That is, upon bursting itis desired that the dome 40 tear away from the flange portion 41 alongthe groove 44 and that portion of the transition region 42 which iscoextensive with the groove 44, while preferably the tab region 45remains intact or untorn.

FIG. 4 shows a cross-sectional view including a portion of thetransition area 42 having a groove 44 therein and FIG. 3 shows across-sectional view of a portion of the transition region 42 which doesnot include a groove. It is noted that preferably the upstream supportring 17 extends radially outward from approximately the center of thegroove 44. In contrast, the support ring 16 extends radially inward ofthe transition region 42 so as to support the transition region 42 atleast in the portion thereof including the groove 44. The support ring16, as is seen in FIG. 6, includes the arcuate projection 34 which isdownstream of and preferably aligned with the tab region 42 such that,when the rupture disc 18 bursts the dome 40 will pivot about the hingeregion 42 and engage the arcuate projection 34, as is shown in FIG. 7wherein the ruptured and somewhat crumpled dome, as indicated by thereference numeral 46, wraps about the projection 34 especially in thearea of the edges 47 of the dome 46 that tore from the flange portion 41but which were adjacent the hinge region 42. The projection 34 isarcuate along its radially inward edge 48. The arcuate projection 34 hasradially outward ends thereof 49 and 50 which include an arctherebetween which is generally similar to but slightly larger than thearc encompassed by the tab region 45.

Shown in FIGS. 8, 9, 10 and 11 is a first modified embodiment of thepresent invention including a first modified rupture disc 100 andsupport ring therefor 101 which are suitable for use in the assembly 1as alternative replacements for the disc 18 and support ring 16respectively. The support ring 101 is essentially similar to the supportring 16 and includes an arcuate projection 102 which extends radiallyinward therefrom. The arcuate projection 102 is downstream aligned witha tab region 103 of the disc 100. The disc 100 includes a dome 106 witha radially outward extending flange portion 107 joined by a transitionregion 108. A partially circumferential, relatively deep groove 112extends entirely around the dome 106 except in the tab region 103wherein there is a very shallow groove 113 compared to the relativelydeeper groove 112. An indentation 114 is positioned in the dome as isbest shown in FIG. 9. The indentation 114 is approximately centered onthe tab region 103 and is spaced closely therefrom. The indentation 114comprises an elongate dent which is oriented approximately parallel tothe transition region 108.

FIGS. 12 and 13 show a second modified disc 130. The disc 130 is similarto the disc 100 except that instead of an elongate indentation 114, asseen in disc 100, the disc 130 has a dimple or dot indentation 132 onthe dome 131 thereof. The disc 130 has a flange portion 133 andtransition region 134 which are similar to the same features in the disc100 in the previous embodiment. A tab region 135 is centered to bealigned with the indentation 132.

FIG. 14 shows a third modified rupture disc 140 according to the presentinvention including a dome 141 having an elongate indentation 142therein. The disc 140 is similar to the disc 100 except for theplacement and size of the indentation 142 as compared to the indentation114.

FIG. 15 shows a fourth modified rupture disc 150 according to thepresent invention. Disc 150 includes a dome 151, a flange portion 152,and a transition region 153 between the flange portion 152 and the dome151. A tab region 154 is specifically shown, and this disc 150 has anon-tab region (not shown) in the transition region 153 similar to thatof the disc 100. The disc 150 also has a transition region with aslightly increased radius of curvature generally indicated by the arrow155 in a portion of the transition region 153 as compared to theremainder thereof and specifically in the tab region 154.

FIGS. 16 through 26 illustrate different steps in the method ofmanufacture of a rupture disc of the present invention and illustratevarious structures utilized in the manufacture of the present invention.FIG. 16 illustrates a planar sheet of metal or blank 200 from which arupture disc, such as the previously described disc 18, is manufactured.FIG. 29 illustrates an apparatus 203 for forming a rupture disc fromsuch a blank 200.

The apparatus 203 includes a lower member 204 and an upper member 205which generally mate together so as to define a chamber 206therebetween. A first sealing ring 209 is placed in a bottom of thechamber 206 followed by the planar sheet of metal 200 followed by atleast one additional bulge forming ring 210. Preferably the outerdiameter of the rings 209 and 210 and the blank 200 are approximatelythe same as the inner diameter of the chamber 206 where theyinterengage. A hydraulic fluid supply passage 211 communicates with asuitable source of hydraulic fluid through a hydraulic hose 212 with alower portion 207 of the chamber 206, which chamber portion 207 is shownbelow the blank 200, to be pre-bulged into a domed rupture disc 213. Itis noted that the blank 200 is not shown in FIG. 29 but the blank 200occupies the same region as a flange portion 214 of the disc 213 as wellas the region surrounded by the flange portion 214. After the blank 200is placed in the apparatus 203, fluid is forced into the chamber portion207 through the passage 211 while the disc blank 200 is securely heldabout the edges thereof in position so as to pre-bulge into the disc213. FIG. 17 shows the disc 213 and the upper ring 210. As shown in FIG.21, a lower inner radial edge 218 of the ring 210 defines an outerboundary or periphery 219 of a dome 220 of the disc 213. It is notedthat the edge 218 is a sharp edge formed by sides of the ring 210 whichmeet at almost 90 degrees with respect to one another. FIG. 22 shows aview which is similar to FIG. 21 except it is taken at another locationalong the ring 210 whereat the sides of the ring 210 join in a roundededge 222 which defines the limits or periphery 223 of the dome 220 atthat location. A transition region 224 shown in FIG. 22 has a largerradius of curvature at that location than a transition region 225 shownin FIG. 21. This change in radius and/or slope is similar to the conceptpreviously shown in and described for FIG. 15.

Shown in FIG. 27a is an alternative ring set 230 for use in conjunctionwith the apparatus 203 in place of the ring 210. The set 230 shown inFIG. 30 in conjunction with a disc 235 includes a lower forming ring 231similar to the ring 210 and an upper indentation ring 232 which has asimilar internal diameter to the ring 231 but is positioned somewhateccentrically thereto. The ring set 230 is utilized in the production ofthe rupture disc 235, shown in FIG. 28a, having an indentation 236thereon produced by a radially inward and lower edge 238 of theindentation ring 232 engaging the disc 235 as same is pre-bulged. Anouter portion of the ring 232 is removed so that the ring set 230 has anoverall outer diameter approximating the diameter of the disc 235 sothat the ring set 230 and disc will set in the apparatus 203 withoutlateral slippage therebetween when the disc 235 is being bulged.

FIG. 27b shows a second offset ring set 250 having a lower forming ring251 which is generally concentric with an upper indentation ring 252.FIG. 28b shows a rupture disc 255 manufactured in the apparatus 203wherein the ring set 250 has been substituted for the ring 210. Anindentation 256 is formed on the rupture disc 255 by a radially inwardextending projection 257 having an inner surface 258 with a lower edgewhich engages the disc 255 during pre-bulging and produces theindentation 256. The surface 258 is arched to approximate the arc of thedisc 255 where they engage and includes linear feathering on oppositesides of the surface 258.

FIG. 27c shows yet another ring set 260 having a lower forming ring 261and a generally concentric upper indentation ring 262. FIG. 28c shows arupture disc 265 manufactured in the apparatus 203 wherein the ring 210has been replaced by the ring set 260. The upper indentation ring 262includes a radially inwardly extending projection 267 generallycomprising a chord or a linear joining of the two sides of the ring 262and having an inner surface 268 with a lower edge which engages a disc265 (FIG. 28c) during pre-bulging thereof so as to form an indentation266 therein.

After pre-bulging and indenting (where done) in the apparatus 203,rupture discs, such as the disc 300 in FIG. 23, which were manufacturedin the apparatus 203 are removed. The disc 300 has an indentation 301thereon and a tab region 302 located in close association to theindentation 301. The disc 300 is then joined with an upstream supportring 311 and a downstream support ring 310. The rings 310 and 311 aresimilar to rings 16 and 17 shown in FIG. 1. The downstream ring 310includes an arcuate projection 312 which is aligned to be centeredrelative to the tab region 302 and the indentation 301. The disc 300 andthe rings 310 and 311 are then preferably joined together by welding orthe like as shown in FIGS. 24 and 26 after groove 314 is formed in atransition region 315 thereof.

A grooving apparatus 330 for performing the grooving process is shown inFIGS. 18, 19 and 20. The apparatus 330, as shown in FIG. 18, includes anupper holder member 331, a lower holder member 332 which mates with theupper holder member 331, a die or knife holding member 333, and pressureexerting means such as the partially shown hydraulic press mechanism334. A pre-bulged disc 337 is placed in a seat 338 in the upper holdermember 331. The knife holding member 333 includes a circular knife 340having an upper edge 341 and having a radius slightly larger butapproximately the same radius as the inner edge of a transition area 348of the disc 337. The knife edge 341 is placed in engagement with thedisc transition area 348, as shown in FIG. 19, and pressure is appliedby the press 334. Stops 349 on the knife holding member 333 engage theupper holder 331 to facilitate proper grooving of the disc 337 so thatthe groove 350, as seen in FIG. 19, has a proper depth associatedtherewith. The knife 340 shown in FIG. 20 is only partiallycircumferential and includes a sector 360 in which the knife 340 isomitted to leave a portion of the disc transition area 348 ungrooved.The stops 349 are removable from the knife holding member 333 tofacilitate alternative use of the other stops specifically designed forother particular depths and/or other disc thicknesses.

Alternatively, the knife 340 can be replaced by a completelycircumferential knife member or also, alternatively, by a knife member357, as shown in FIG. 31, which is completely circumferential but for aportion 358 of the edge 359 of the knife blade which has been furtherrounded or had a portion of the edge removed so as to limit the depth ofa groove in that region where the portion 358 engages the disc 337. Theside of the knife in FIG. 19 diverge from the edge 341 at an angle ofapproximately 60 degrees relative to one another and the cutting orgrooving edge 359 has a radius of approximately 0.005 inches.

FIG. 25 shows an enlarged section of a rupture disc 380 having lowersupport ring 381 and an upper support ring 382 associated therewith. Thedisc 380 has had a groove 383 according to the present invention placedin a transition region 384 thereof. The groove 383 was produced by amethod similar to the groove 380 formed in the process shown in FIGS. 18through 20. The groove 380 includes side walls 381 and 382 which divergewith respect to each other and at about 30 degrees each to an axis orvertical line bisecting the groove 380 and are joined by a connectingsurface 383 having a radius of approximately 0.005 inches. The disc 380has a dome 389, a periphery 390, a concave side 391 and a convex side392.

It is to be understood that while certain forms of the present inventionhave been illustrated and described herein, it is not to be limited tothe specific forms or arrangement of parts described and shown.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. A method of manufacturing a reverse buckling rupture disccomprising the steps of:(a) providing a disc support structure includinga source of hydraulic fluid; (b) placing a generally circular and planarblank to be formed into said disc in said support structure such thatsaid hydraulic fluid source communicates with only one side of saidblank; (c) placing a forming ring on the side of said blank opposite theside thereof communicating with said hydraulic fluid; said forming ringbeing generally annular in shape and having an interior diameterapproximately equal in length to a projected peripheral diameter of adome of the disc to be formed; (d) applying sufficient pressure to saidforming ring to maintain said ring in position with the adjacent portionof said blank; while (e) simultaneously applying a preselected pressureto said hydraulic fluid such that a dome portion of said blank bulgesthrough said forming ring thereby producing a disc having a pre-bulgeddome, a flange portion surrounding said dome, and a transition regionbetween said flange portion and said dome; said dome including a crown;and (f) applying pressure to said dome in an unsymmetrical manner at alocation spaced from both said transition region and said crown so as toform an indentation thereon.
 2. The method according to claim 1wherein:(a) pressure is applied to said dome to form said indentation atthe same time as said dome is being bulged through said forming ring. 3.The method according to claim 2 including the steps of:(a) providing anindentation ring spaced from said transition region and having aradially inner edge; and (b) fixedly positioning said indentation ringrelative to said forming ring such that upon bulging of said dome, saiddome is forced against said indentation ring inner edge so as to formsaid indentation thereon.
 4. The method according to claim 1 includingthe step of:(a) applying a groove to said transition area of said discafter the bulging of said dome.
 5. The method according to claim 4including the steps of:(a) after forming said dome, removing saidindentation ring and said forming ring from engagement therewith; and(b) applying a die having a knife edge in the desired configuration ofthe groove to said transition region under pressure so as to form saidgroove.
 6. The method according to claim 1 including the steps of:(a)supplying a forming ring which has an interior surface and a sidesurface which meet at substantially right angles so as to form a sharpedge therebetween; and (b) rounding a sector of said edge prior toforming said disc so as to increase the radius of the transition regionadjacent to the sector of said edge wherein the edge was rounded.
 7. Amethod of producing a pre-bulged reverse buckling disc having a dome, aflange connected to and extending radially outward from said dome and atransition region connecting said dome and said flange, and furtherwherein said transition region in radial cross section has a firstradius in a first sector of said transition region and a secondincreased radius in second sector of said transition region; said methodcomprising the steps of:(a) supplying a generally planar blank to beformed in said disc; (b) placing a forming ring, having a interiordiameter of approximately the same length as the desired peripheraldiameter of the dome of the disc, on one side of said blank with aninterior edge of said ring engaging the disc; said ring having a firstsection associated therewith wherein said edge is formed by walls joinedat approximately 90 degrees and a second section wherein said edge isformed by walls joined with a connection having a substantial radius;and (c) applying pressure to the side of said disc opposite said ring soas to bulge said disc through said ring thereby forming said dome andsaid transition region; said transtion region having a first radius inthe region adjacent said edge first section and a second increasedradius as compared to said first radius in the region of said transitionregion adjacent said edge second section.
 8. A method of forming agrooved area in the transition region of a rupture disc comprising thesteps of:(a) forming a pre-bulged disc having a dome, a flange extendingradially outwardly from said dome and connected thereto, and acircumferential transition region connecting said dome and said flange;(b) placing a die including a knife blade with a circumferential knifeedge having a diameter approximately equal to the diameter of saidtransition region on said disc so as to surround said dome and such thatsaid edge engages said transition region; (c) applying a force to saiddie along a central axis of said disc such that said edge penetratesinto said transition region; and (d) providing stops to limit the depthof penetration of the knife edge into the transition region.
 9. Themethod according to claim 8 wherein:(a) said knife blade has asubstantially constant knife edge along the circumference thereof. 10.The method according to claim 8 wherein:(a) said knife blade includes afirst sector therealong having an edge with a first depth of penetrationassociated therewith and a second sector therealong with an edge havinga second depth of penetration associated therewith such that said firstdepth of penetration is substantially greater than said second depth ofpenetration; and (b) said method includes the step of: applying a forceto said die until said knife edge first sector penetrates to said firstdepth and said second sector penetrates to said second depth therebydefining a tab region.
 11. The method according to claim 9 wherein:(a)said knife blade includes an inner wall adjacent said edge secondsector; and (b) said method including the step of: (c) engaging saidinner wall with said transition region in the area of said second sectorof said knife blade edge during the groove forming step so as to modifythe radially cross sectional radius of curvature of said transitionregion in the area associated with said knife blade second sector.